It is often desirable to obtain objects, such as aggregates of gravel (e.g., stones, rocks, pebbles, gemstones, and the like), for use in decorative concrete for pools, sidewalks, landscaping, and the like. Such gravel aggregates may comprise stones of one or a few colors, or a number of different colors, as desired.
One way to obtain colored stones is to mine it from quarries as crushed aggregate. However, due to the complexities of geology, stones mined from a quarry generally comprises stones of a number of different colors. Thus, to obtain stones of a particular desirable color or number, range, and/or blend of desirable colors, stones of desirable colors mined from a quarry must be separated from stones of undesirable colors and/or multiple colors.
Stones of desirable colors may be separated manually (i.e., by hand) from stones of undesirable colors and/or multiple colors, but such a manual method is very laborious and, as a result, expensive and impractical. Therefore, it is preferable to mine stones of desirable colors from quarries that have a geology yielding a propensity of stones of desirable colors. Locating such a quarry, however, may require traveling great distances and expending substantial sums of monetary resources. It is not uncommon for such quarries to be located hundreds of miles from where such gravel is needed, or even overseas, necessitating the transportation of such gravel over great distances to desired locations.
Even when quarries are located that have a propensity to produce stones of desirable colors, there are often stones of undesirable colors that are mixed in with the stones of desirable colors. Thus, stones of desirable colors must still be separated from stones of undesirable colors.
As mentioned above, stones of desirable color may be separated manually (i.e., by hand) from stones of undesirable color and/or multiple colors by hand. Manual separation, however, is extremely laborious, and thus expensive. For example, a decorative stone facility typically separates and blends more than 10,000 tons of aggregate per year. For half-inch stones, 10,000 tons would require processing about 30 tons of stones per day. At 70 stones per pound, approximately one billion stones would need to be examined and separated each day! This is not economically feasible using manual techniques. Even if such quantity of stones could be feasibly examined and separated manually each day, it would not only be extremely laborious, and thus expensive, but also prone to yield inconsistent results.
In an alternative to quarries, water streams and rivers often provide stones in a collage of different colors. Furthermore, stones found in streams and rivers are also generally mixed, cleaned, and polished and, therefore, generally preferable to stones obtained from quarries. The more varied the geology of an area upstream from a gravel deposit, the more varied the colors of stones found in streams and rivers. The streams and rivers have not only provided a variety of colors but, in many cases, have also transported them closer to decorative aggregate markets, thus reducing transportation costs. However, to obtain stones of particular colors or range of colors, the stones must still be separated. Separation may be accomplished by hand but, as discussed above, manual separation is very laborious, expensive, and prone to inconsistent results.
In an alternative to obtaining stones from select quarries, streams, and/or rivers, and using manual separation techniques, mixtures of stones (or any type of objects or items) of multiple colors may be automatically separated by color using various automated mechanical systems. Such systems that separate stones based on color are, however, binary systems. That is, such systems either accept or reject a stone (or other object) of a certain color from a stream of stones. Such binary systems are, however, not only inadequate to separate the quantity of stones discussed above, but are also inadequate to separate gravel into multiple categories of colors.
Therefore, what is needed is a system and method for efficiently separating large quantities of objects, such as stones, into multiple categories of colors, or other characteristics, such as shape, mineralogy, reflectivity, angle of refraction, radioactivity, and the like.